1. Technical Field
The invention relates to a light emitting device and the fabricating method thereof. In particular, the invention relates to a light emitting device with a light extraction layer, that can reduce the difference in the refractive index between the emitting layer and the packaging layer by embedding a light extraction layer that matches the refractive index. The invention also relates to the fabricating method thereof.
2. Related Art
With prosperous development and energy-saving concept in semiconductor technology in recent years, using light emitting diodes (LED's) to replace traditional illumination and display devices has been widely accepted. It even has become one of the most noticeable industries.
Generally speaking, traditional LED does not have a matching refractive index between the light emitting material (i.e., emitting layer) and air or packaging glue (i.e., packaging layer). Therefore, most photons are totally reflected. Photons can penetrate through the packaging layer only when the incident angle is less than the critical angle, thus visible to eyes. The photons that cannot go through are absorbed by the LED, resulting in bad light emitting efficiency. Take the most popular blue LED material, GaN, as an example. Its refractive index nGaN is roughly between 2.5 and 2.8. Another blue LED material InGaN has a refractive index nInGaN around 3.3. The red LED material GaAs has a refractive index nGaAs around 4. The refractive indices of the above-mentioned materials have a large difference from that of the air or packaging layer. It is helpful to extract photons inside the LED if we could reduce the difference between the refractive indices of the emitting layer and the external medium (e.g., air or packaging layer).
In view of this, some vendors propose to use packaging glue with a high refractive index as the packaging layer of the LED. The packaging glue may even be doped with materials with a scattering mechanism, such as fluorescent powders, TiO2 powders, etc. Besides, some vendors also change the packaging structure of the LED to reduce total reflection, thereby increasing light output efficiency. However, using packaging glue with a high refractive index as the packaging layer costs a lot and is not easy to obtain. Changing the packaging structure of the LED increases packaging difficulty and reduces the yield. Therefore, the above two methods cannot effectively solve the problem with bad light emitting efficiency.
In summary, the prior art always has the problem of being unable to effectively increase light emitting efficiency of LED. It is imperative to provide a better solution.